The present invention relates to an aminopolycarboxylic acid chelating agent, heavy metal chelate compound thereof and method for processing silver halide photosensitive materials with them. In particular, the present invention relates to a novel chelating agent for masking metal ions harmful to new bleaching agents and photographic processing agents used in a bleaching or bleach-fixing step after the treatment with a color developer.
Photosensitive materials are exposed, color-developed and then processed with a processing solution having a bleaching function. As the bleaching agents contained in the processing solution having the bleaching function, ferric complex salts are widely known. Among the ferric complex salts, ferric complex salts of ethylenediaminetetraacetic acid (EDTA) has been known from old times. Ferric complex salt of 1,3-propanediaminetetraacetate (1,3-PDTA) having a stronger bleaching function has been widely used since several years ago. Although the rapid processing properties of ferric complex salt of 1,3-PDTA are superior to those of ferric complex salt of EDTA, the bleach fog is easily caused by a strong oxidizing power thereof, and the image-storability after the process is easily impaired (magenta stain is increased). Another problem is that because of a high oxidation-reduction potential, the decomposition is accelerated with time in a thiosulfuric acid-containing system to form sulfur. As the recognition of the global environmental safeguards is being improved recently, a bleaching agent usable in place of difficultly biodegradable ferric complex salt of EDTA and ferric complex salt of 1,3-PDTA is being developed in the photographic field in which the development of a processing agent which causes as low as possible environmental pollution demanded. The metal complex salts are usable not only as a component of a composition of a bleach-processing solution but also as that of an after-treating composition used for the intensification, reduction or toning. However, they also have the problem of the poor biodegradation.
As the compounds capable of solving these problems, those described in Japanese Patent Unexamined Publication (hereinafter referred to as "J.P. KOKAI") Nos. Hei 5-72695 and 5-303186 were developed. However, it has been found that when such a compound is used, another problem occurs in some cases. For example, when a ferric complex of ethylenediaminebissuccinic acid (EDDS) described therein is used as the bleach-fixing agent, problems such as insufficient recoloring and Blix discoloration occur. A further effort must be made for solving this problem.
As the photographic process is conducted at various places ranging from a large-scale processing laboratories having a large automatic developing machine to a photo processing shops called "mini-labs" having a small automatic developing machine, the processing efficiency tends to be lowered in some cases.
One of the main causes of this problem is the contamination of the processing solution with a metal ion. The ill effects of the incorporated metal ion, which vary depending on the kind of the ion and processing solution, are the clogging of a filter in the circulation system of the automatic developer, staining of the film in the course of the process and decomposition of a color developing agent, black developing agent such as hydroquinone or monol and a preservative such as a hydroxylamine or sulfite. As a result, the photographic properties are seriously impaired.
A chelating agent which masks the metal ion has been used for solving the above-described problems in the art. The chelating agents include, for example, aminopolycarboxylic acids (such as ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid) described in Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") Nos. Sho 48-30496 and 44-30232; organophosphonic acids described in J.P. KOKAI Nos. Sho 56-97347 and 56-39359 and West German Patent No. 2,227,639; phosphonocarboxylic acids described in J.P. KOKAI Nos. Sho 52-102726, 53-42730, 54-121127, 55-126241 and 55-65956; and compounds described in J.P. KOKAI Nos. Sho 58-195845 and 58-203440 and J.P. KOKOKU No. sho 53-40900. Although some of these compounds have already been practically used, the efficiency of them was not yet satisfactory.
Compounds having a skeleton similar to that of the compounds of the present invention include ethylenediamine-N,N'-disuccinic acid described on pages 309 to 311 of "Chelate Kagaku (Chelate Chemistry)" (5) written by Kagehei Ueno and published by Nanko-do.
The masking capacity of this compound is easily variable depending on pH and, therefore, the capacity is not on a satisfactory level when the conditions of the treating solution are varied in many cases. Particularly in an alkaline developing bath in which the masking capacity of this compound for iron ion is essentially low, an excess amount of the compound is necessitated, which is photographically undesirable. Particularly, as the social demand of the environmental protection is increasing recently, the amount of the replenisher for the photographic processing solution is being further decreased and, therefore, the residence time of the processing solution in the processing machine becomes longer. In addition, as the rapid process is demanded, the concentration of the developing agent, bleaching agent and fixing agent tends to be increased and the temperature of the processing solution also tends to be elevated. Thus the deterioration in the long-time storability is becoming serious.
Further, as the concentration of the processing solution is increased for the purpose of accelerating the process, the changes of the conditions (mainly pH) become more serious. As a result, the effect of the metal-masking agent is reduced disadvantageously. Under these circumstances, the development of a more excellent, new chelating agent capable of effectively masking the metal even under unstable conditions is demanded.